Generally you can install any distribution which supports UEFI. We provide the OEM iso-images for transparency reasons, as those are the ones being used for installation before they are shipped. They differ just marginally from the original iso images with things like: oem start (on first boot set up a user etc.), nitrokey-app is pre-installed, some amazon ads are removed. You can see the details on github in the repositories ending with -oem, e.g., https://github.com/Nitrokey/ubuntu-oem